In the manufacture of concrete and other cement derivatives, there are various techniques for developing high initial strength when the aim is to achieve rapid stripping or to put works into service quickly.
One of the most common techniques for achieving these high initial strengths involves using a high dosage of cement in the concrete. In this respect, it should be borne in mind that the maximum content of cement in concrete is limited to approximately 400 kg/m3, in order to reduce the negative effects of hydraulic and thermal shrinkage. There is also an upper limit for the values of some concrete components, such as, for example, alkalis and tricalcium aluminate (C3A) which come mainly from cement in order to avoid possible pathologies in concrete such as the alkali-arid reaction (alkali silica reaction ASR) and that of secondary ettringite (delayed ettringite formation DFR). This implies that the use of high quantities of cement leads to high quantities of these components, which can also compromise the durability of the concrete. In addition, this technique involves a high cost and from the environmental point of view it is not highly recommended due to the high emission of CO2, and the large amount of raw materials and energy that are needed.
Another one of the most widely-used techniques for achieving high strength at short ages involves the thermal treatment of concrete. In Calleja, J. “Heat treatments with concrete”, Construction reports Vol. 120, 193, 1967, the thermal treatment of concrete is described using various techniques, such as the preheating of materials, immersion in hot water, steam curing and electrical heating. In spite of being a very effective system, it requires significant investments, with high costs due to energy sources such as electricity or steam. In addition it is a system that, for the above reasons, only applies to fixed installations, mainly prefabrication, which account for a very low percentage of cement derivatives.
Another known way of accelerating the performance of cement derivatives is the use of “accelerating” chemical additives such as calcium chloride or calcium formate, among others. The document “Effect of calcium formate as an accelerator on the physicochemical and mechanical properties of pozzolanic cement pastes”, Cement and Concrete Research June 2004; 34(6), 1051-1056 describes how adding calcium formate to cement shortens the initial time and increases the compressive strength and combined water content.
The main function of these additives is to promote hardening, although they can also accelerate setting. This means that both the setting time and hardening time have to be controlled, which is extremely complicated in practice, mainly due to the large influence of small variations in temperature and product composition. In practice, these accelerators have been discarded mainly in practice because of the problems of workability and durability.
Other additives that can be added to concrete to increase its compressive strength include plasticisers and superplasticisers. This strength is inversely proportional to the amount of water added. Therefore, in order to produce more resistant concretes, the amount of water is considerably reduced, which results in mixtures that are difficult to handle, and it is necessary to add plasticising and superplasticising additives. It is a technology used and is very effective, especially for achieving high final strengths (28 days), but has very important limits to short ages, especially when they are less than 24 hours.
The use of so-called “special cements” has also been described in order to achieve high compressive strengths over short periods. These cements are cements that, in addition to complying with the physical, mechanical and chemical specifications established by the UNE-EN 197-1:2000 standard with respect to common cements, have more demanding requirements with respect to certain characteristics of the same, such as, for example, one-day strength, granulometry and high fineness. Thus, for example, in document ES2438621 B2, a cement with high mechanical performance at short ages is described. Its composition includes C3A in a proportion of 0 to 3%, and C3S in an amount greater than 80%, which is a sulforesistant cement.
Although the use of these special cements constitutes a very interesting alternative for obtaining cement derivatives with high strength in short times, the cost associated with it is very high and, as we will see later, a waste of its properties in most cases.
It would therefore be desirable to find an alternative that overcomes the shortcomings indicated above. In other words, it would be desirable to find an alternative to existing cement derivatives, such as concretes, mortars and slurries, among others, that would allow the development of high compressive strengths at times of less than 24 hours, while being economical environmentally viable and technically acceptable due to the state of the art in the technology of cement derivatives and their Regulations.